Dale Carnegie called his self-help book, written at the nadir of the Great Depression, How to Win Friends and Influence People, as if it were a relationship manual. But it’s no accident that at the outset he introduces Charles M. Schwab, head of U.S. Steel,

one of the first people in American business to be paid a salary of over a million dollars a year (when there was no income tax and a person earning fifty dollars a week was considered well off) . . .

Nor is it an accident that when he was etching his public profile, Carnegie decided to take advantage of a lucky homophony, casting off his father’s “Carnagey” for the spelling used by Schwab’s famous boss Andrew. Even if he didn’t dare utter its name, Carnegie knew the pathology he was treating: money-deficit disorder.

By invoking these winners, Carnegie no doubt meant to persuade his readers that the words he was about to reveal — the key to Schwab’s success, according to the million-dollar man himself — would “all but transform your life and mine if we will only live them.” The secret? “ ‘I consider my ability to arouse enthusiasm among my people,’ said Schwab, ‘the greatest asset I possess.’ ” And how did Schwab do it? According to Carnegie, anyway, by never criticizing others, by giving “honest and sincere appreciation,” thus “arous[ing] in the other person an eager want.” Updating, if unconsciously, Jesus’ injunction about neighborly love, the book promises that if you harness these erotics, you can’t help but succeed.

The Dale Carnegie who emerges from Self-Help Messiah, Steven Watts’s fine new biography, is more than an übersalesman dispensing tricks of the trade to the Willy Lomans of midcentury America. He is an apostle of a new gospel preached to the new man who emerged toward the end of the nineteenth century. His fate was no longer in the hands of an angry God, or even a benevolent God who would bestow happiness in the hereafter; nor did he have to settle for whatever station he had been born into. Self-invention was the new route to salvation, and if he failed to take it, he would be condemned to the earthly equivalent of what awaited Calvin’s sinners — the hell of economic and social failure.

The self unbound from divine destiny was bound to be anxious about exactly what it was supposed to be doing with itself, and long before Carnegie wrote his book, phrenologists, Christian Scientists, theosophists, Emersonians, Swedenborgians, and mesmerists had fanned out across the country to hawk cures for this modern worry, promising surefire ways to achieve health and wealth amid the hurly-burly of a free country. For all their differences, these philosophies have gone down in history as the various tributaries of the New Thought movement, united by their faith in “mind power.” As Watts describes them, New Thinkers as disparate as Christian Science’s Mary Baker Eddy and the animal magnetist Phineas Quimby “believed that hidden mental resources could be retrieved and mobilized to increase emotional vigor, social success, and material accumulation” and offered their own methods for tapping these resources.

Carnegie was born in 1888 in Missouri to a “hardscrabble farmer” father and a “devout and dynamic lay preacher” mother. The family, as he recounted years later, lived through floods that wiped out their crops and diseases that ravaged their hogs until, after “ten years of hard, grueling work,” his parents were “not only penniless, [but also] heavily in debt.” Those hard times had left their mark. “I was full of worry in those days,” Carnegie once wrote — a chronic state that he later called an “inferiority complex” and that Watts explains as the unsurprising outcome of “the ongoing tension between poverty and piety” inflicted on a “sensitive child [who] could not understand why their efforts, and their upstanding values, seemed to produce only failure.” To the young man emerging from this childhood misery, the New Thought promise that all adversity could be overcome through strength of mind was irresistible.

Carnegie first encountered these ideas in 1904, when he enrolled at the State Normal School in Warrensburg, Missouri. As he later recounted,

I studied biology, science, philosophy, and comparative religion. I read books on how the Bible was written. I began to question many of its assertions. I began to doubt many of the narrow doctrines taught by the country preachers . . . I stopped praying. I became an agnostic. I believed that all life was planless and aimless. I believed that human beings had no more divine purpose than had the dinosaurs . . . I sneered at the idea of a beneficent God who had created man in his own likeness.

Carnegie was surrounded by exemplars of this agnosticism, young men unyoked from piety like his mother’s, free to invent themselves as they pleased.

I looked around and saw that the men who had won the debating and public speaking contests were regarded as the intellectual leaders in college. They were in the limelight . . . Everybody knew them! Everybody knew their names! . . . I said, “maybe I can do that.”

He became a champion college orator, a résumé entry that helped him with his inferiority complex and eventually persuaded his first employer to hire him. Watts tells us that Carnegie was the beneficiary of a change in the nature of competitive rhetoric. Speech-making, once guided by “rules of formal declamation,” had become less constrained and now encouraged “the free play of individualism” and “utiliz[ed] the voice and body for a delivery that was ‘natural.’ ” This shift reflected the larger cultural turn toward the notion of the world as a venue for the efflorescence of the limitless mind. With his preacher’s charisma and conviction, Carnegie was perfectly suited to this new world.

Carnegie’s first stint as a salesman — traveling the Midwest selling correspondence courses to farmers — was a bust that left him penniless and sobbing in his rented room, but even when he found success selling bacon and soap for Armour and Company in the northern prairie, he longed for the self-expression he had enjoyed in college and the modest celebrity it had bestowed on him. He aspired to the traveling-lecturer circuit and set his eyes on Chautauqua. When he described this ambition to an Episcopal priest he met in the caboose of a freight train (and Watts’s story is full of just this kind of delicious detail), the priest suggested he go to the American Academy of Dramatic Arts in New York City, a school whose alumni would eventually include actors ranging from William Powell to Robert Redford.

At the academy, Watts tells us, Carnegie learned that acting was “an expression of the ‘total man’ — the union of imagination, mind, feeling, and technique.” Soon he was playing multiple roles in the romantic melodrama Polly of the Circus for crowds around the country, but within the year he had decided that theater life was too uncertain for him. After a series of unsuccessful car-sales jobs left him broke once again, Carnegie decided to put his expressive skills to work teaching public speaking at YMCAs in New York and other cities, an endeavor that by 1915 had proved popular enough to spur the publication of his first self-help book, The Art of Public Speaking.

That book signaled the themes that would eventually make Carnegie’s fortune. “We choose our characters by choosing our thoughts,” he told his readers. By “character” Carnegie meant something other than the “old-fashioned, Victorian standard with stern moral values and genteel decorum,” Watts explains. After the dislocations of the fin de siècle, the struggle to refine character out of the raw ore of humanity was giving way to the struggle to develop what psychologists were just beginning to call “personality” — that malleable set of traits whose “social masks,” as Carnegie wrote, “could be taken off and on at will.” Putting on a mask had its own rigors: “You must actually ENTER INTO the character you impersonate, the cause you advocate, the case you argue — enter into it so deeply that it clothes you, enthralls you, possesses you wholly.” This protean confidence, Carnegie said, must be balanced by an appearance of humility, so as to flatter the listener — “self-preservation is the first law of life, but self-abnegation is the first law of greatness . . . Dynamite the ‘I’ out of your conversation” — and yield the “emotional force” that allows one man to arouse want in another.

The ideal self may have been a cipher, but there was one quality that we all shared and that made self-abnegation a winning strategy. The downcast, the depressed, the discouraged — people only wanted to be well-liked. Earlier in the twentieth century, the worried masses had been driven to doctors for their hysteria and neurasthenia, but by 1936, when How to Win Friends was published, patent medicines and rest cures had fallen out of favor as treatments for middle-class malaise. Carnegie thought he knew why. “Many persons call a doctor when all they want is an audience,” he wrote. If those earlier cures had worked, it was only because they had inadvertently satisfied this need for recognition.

How to Win Friends was an almost immediate success, amassing sales of 250,000 copies in its first three months and more than 30 million in the next few decades. Shedding the arcane metaphysics of New Thought in favor of the hardheaded pragmatics of American business, Carnegie provided precisely the therapy a nervous populace needed — and, to judge from the book’s continued annual six-figure sales, the therapy it continues to need. He also opened the way for all the self-help gurus to come, from Napoleon Hill, whose Think and Grow Rich came out in 1937, to Stephen Covey, whose 7 Habits franchise still fills airport-bookstore shelves, to The Secret, the book and movie that partially restore those metaphysics, promising that the universe is governed by a law of attraction that returns our positive thoughts to us in the form of health and, especially, wealth.